1. Field of the Invention
The present invention relates to a method of graft polymerization by which can be formed a graft structure in which all of the polymer chains are directly bonded to the polymerization initiating layer.
The invention also relates to a variety of uses to which the above-mentioned method of graft polymerization is applied. That is, the invention relates to highly hydrophilic members applicable to a variety of uses; i.e., a highly sensitive and reduced scumming printing plate precursors which are adaptable to both of positive and negative types; pattern forming materials and a pattern forming method in which positive and negative patterns can be formed in a convenient operation; as well as highly sensitive and reduced scumming planographic printing plate precursors which need no development process and are adaptable to both of the positive and negative types. Moreover, the invention relates to pattern forming materials and a pattern forming method, as well as planographic printing plate precursors, in which a pattern can be formed directly by operating infrared laser based on the digital signals. Moreover, the invention relates to a method of producing a particle-adsorbed material, in which a particle-adsorbed material having functional surfaces prepared by adsorbing a variety of functional particles such as surface roughing members, electrically conductive members or shading members. The invention also relates to a method of producing a metal particle-dispersed thin layer film in which a metal particle-dispersed thin layer film is prepared by forming a thin film of metal particles, i.e. silver or copper particles, on a substrate, to thereby obtain a dense, highly durable and highly productive metal particle-dispersed thin layer film useful as anti-electromagnetic wave film or magnetic film.
2. Description of the Related Art
In convwentional graft polymerization, for example, as desclosed in Hiroo Iwata “Surface”, vol.32, No.3, Mar. 1, 1994, Koshin-sha, p.190–196, most methods have been based on graft formation using an active point formed by irradiation of plasma, γ-ray or EB mainly to an organic substrate. Since a large-scale apparatus such as a plasma, γ-ray or EB generator has to be used in this method, it has been desired to provide a more convenient method of graft polymerization.
In order to solve this problem, a technique using UV irradiation for graft polymerization has been proposed. As such a technique, for example, there is a method in which a polymerization initiator having a functional group chemically bonded to the substrate surface is allowed to react on a glass substrate or an organic substrate having a reactive group on the surface to immobilize the initiator on the surface, and the substrate is then irradiated with UV to carry out graft polymerization. In one method, for example, a terminal silane-coupling agent having an initiator is reacted with a glass substrate to form a sol-gel layer so as to obtain a glass substrate whose surface is modified with the initiator, and the obtained glass substrate is immersed in a monomer solution and then irradiated with UV to carry out graft polymerization (see, e.g., Hiroo Iwata, “Surface”, vol.32, p.190–196, as mentioned above).
In the above-mentioned technique, however, there is a problem in that immobilization of the initiator on the substrate is difficult due to low reactivity because the introduction of the initiator is based on reaction with a solid surface.
In order to solve this problem, some methods for providing a polymerization initiating layer on the surface of a substrate have been proposed. As the technique for the graft polymerization reaction, a method for providing a polymerization initiating layer comprising an initiator and a poly-functional monomer is disclosed in Japanese Patent Appplication Laid-Open (JP-A) No.2000-80189. Additionally, a method for providing a polymerization initiating layer comprising a polymer having a pendent peroxide group for graft polymerization reaction is disclosed in JP-A No. 11-43614.
Other examples of such techiques inclide: a method in which a polymerization initiating layer comprising an initiator and a poly-functional monomer is provided for graft polymerization reaction as disclosed in JP-A No.2000-80189; a method in which a polymerization initiating layer comprising a polymer having a peroxide group is provided for graft polymerization reaction as disclosed in JP-A No.11-43614; a method in which a polymerization initiating layer comprising an initiator and a polymer is provided for graft polymerization reaction as disclosed in JP-A No.53-17407; a method in which a polymerization initiating layer comprising an initiator and a poly-functional monomer is provided for graft polymerization reaction as disclosed in JP-A No.2000-80189; and a method in which a polymerization initiating layer comprising a polymer having a initiating group is provided for graft polymerization reaction as disclosed in JP-A Nos.10-17688 and 11-43614.
The present inventors have investigated these graft polymerization reactions and found that there is a problem in these reactions in that, for example, when a hydrophobic monomer is used in graft polymerization, an initiator contained in the initiation layer or a polymer having the function of initiation is dissolved in a contacting hydrophobic monomer solution because of low capacitity as a film of the initiation layer for polymerization, and as a result, the polymerization occurs in the hydrophobic monomer solution to yield on the surface homopolymer as a by-product which has not been bonded to the initiation layer for polymerization.
A large number of uses are expected by providing hydrophilicity to the surface of a variety of members. Specifically, this can be applied to materials, for example, molded products or biocompatible molded products to which proteins, colloids, bacteria, humin, fats and oils, or air pollutants are scarcely adsorbed, and which are used in such fields as the food industry, medical care (including medical equipment such as artificial organs), the pharmaceutical industry, waste water treatment, coating, printing, and so on; carriers for immobilization which do not make enzymes or cells denatured, or anti-fogging members such as anti-fogging film or anti-fogging coating used in the fields of commerce, agriculture, traffic, household articles, optical instruments, paint, and so on; and surface-hydrophilic members which can be used for static prevention used in fields such asa the electronics industry.
The surface characteristics required for the hydrophilic members used in the above-mentioned fields include repressibility of adsorption of proteins, fats and oils, or humin to the surface of materials, anti-fogging property, biocompatibility, antistatic property, and so on. These functions can be attained by high hydrophilicity. For example, in the field of paint, anti-stain coating to which oily material in rain does not adhere is desired, and in use on a sensor surface, it is desired to provide a surface specifically adsorbing no such materials. An anti-fogging surface on which water drops expand to form a wet state by strong hydrophilicity is required to have high optical transparency and smoothness in addition to the hydrophilicity. Concerning biocompatibility in the medical care field such as artificial organs, the surface is required to inhibit thrombosis, hemolysis, sensitization property, or antigen-antibody reaction. The generation of static prevetion capability by hydrophilicity is particularly important in electronics industry.
As an example of providing hydrophilicity on a surface to satisfy such requirements, a method for grafting the surface of a hydrophilic monomer is known.
The specifically disclosed method (see, e.g., JP-A No.53-17407) comprises coating a hydrophilic radical polymeric compound on the surface of a lipophilic substrate containing as a major component lipophilic resin which contains a certain number of hydrogen groups attached to a carbon-carbon double bond and/or tertiary carbon, and irradiating it with an active ray to form a hydrophilic layer on the surface.
As a process for producing a surface-hydrophilic molded product, however, although the hydrophilic layer is readily made, it is sometimes difficult to coat a hydrophilic radical polymeric compound that is poor in film-forming ability evenly on the surface, resulting in uneven coating in most cases and insufficient hydrophilicity.
Accordingly, a method for grafting a hydrophilic polymer on the surface of a lower layer formed by coating a photo-polymerization initiating layer (photopolymerization initiator comprising a monomer and/or an oligomer) on the surface of a substrate, by supplying energy under contact with a hydrophobic monomer has been developed (see, e.g., JP-A No.10-53658). In this technique, however, there is a problem in that, since the photopolymerization initiator is not firmly fixed in the photopolymerization initiating layer, the initiator contained in the initiation layer is dissolved in a hydrophilic monomer solution during surface graft polymerization, and as a result, polymerization occurs in the hydrophilic monomer solution to yield a homopolymer as a by-product, which has not been bonded to the initiation layer for photo polymerization, on the surface of the layer. This problem is disadvantageous for application to the food industry or biocompatible materials because the homopolymer peels off easily as contaminants from the substrate, having an adverse effect on performance.
In order to solve this problem, for example, in JP-A No. 11-43614, a method for immobilizing a photopolymerization initiator on a layer for initiation of photopolymerization has been proposed. This method comprises using a photopolymerization initiator bonded to polymer. The present inventors have tried to coat this polymer on the substrate surface to carry out the graft polymerization reaction in the same manner as above and found that the polymer to which the photopolymerization initiator is attached is itselfs dissolved in a solution containing the hydrophilic monomer to similarly yield on the surface a homopolymer as a by-product which is not bonded to the photopolymerization initiating layer. Thus, the above problem could not be solved.
The method of planographic printing comprises using a plate material having a lipophilic area receiving ink and an ink-repellent area receiving, not ink but dampening water (hydrophilic region). At present, a photosensitive planographic printing plate pecursor (PS plate) is widely used.
As the PS plate, those in which a photosensitive layer is provided on a support such as an aluminum plate are widely in practical use. On such a PS plate, the sensitized layer of a non-image area is removed by image exposure and development, and printing is conducted thereon utilizing the hydrophilicity on the substrate surface and the lipophilicity of the photosensitive layer of the image area. In the PS plate, the non-image area is required to be removed with no generation of residual film, while in the image area it is required that the recording layer tightly adheres suitably to the support without easily peeling off. Further, in the non-image area, the hydrophilic surface of the support is exposed after removal of the recording layer by development processing, and when the surface of the support has insufficient hydrophilicity, it is spotted due to ink adhering thereto. Therefore, the surface of the support is required to have high hydrophilicity in view of prevention of spots on the non-image area.
As for the hydrophilic substrate used as a support for a planographic printing plate or a hydrophilic layer, an anodically oxidized aluminum substrate, or a substrate or a hydrophilic layer in which the aluminum substrate is further processed with an undercoating agent such as silicate, polyvinylphosphonic acid, or polyvinylbenzoic acid for further improving the hydrophilicity has been used so far (see, e.g., JP-A No.7-1853). Study of hydrophilic substrates or hydrophilic layers using such aluminum supports has actively been conducted. In addition, a technique using a polymer having sulfonic acid groups in an undercoating layer which is formed under photosensitive layers has also been desclosed (see, e.g., JP-A No.59-101651)
On the other hand, concerning the hydrophilic layer on a flexible support such as PET (polyethylene terephthalate), cellulose acetate, and so on, without using such a metallic support as aluminum, the following techniques are known: a swelling hydrophilic layer comprising a hydrophilic polymer and a hydrophobic polymer (see, e.g., JP-A No.8-292558), a PET support having a surface of microporous hydrophilically crosslinking silicate (see, e.g., EP 0709228A1), and a hydrophilic layer cured with a hydrolyzed tetraalkyl orthosilicate containing a hydrophilic polymer (see, e.g., JP-A No.8-272087 or No.8-507727).
Although these hydrophilic layers provide planographic printing plates which can produce printed matter with no scumming at the start of printing, from a practical standpoint it has been desired to further improve the hydrophilicity of the hydrophilic layer to obtain a planographic printing plate precursor producing a printed matter with no scumming even under more severe printing conditions.
In order to solve the above problem, a new hydrophilic layer has been developed utilizing a hydrophilic surface graft layer (see, e.g., JP-A No.2001-166491). In this method, however, there is a problem in production applicability in that a plasma, γ-ray or electron beam has to be irradiated during graft polymerization.
In addition, in order to solve the above problem, another technique has been developed wherein energy is supplied to a lower layer coated on the surface of a substrate with an photopolymerization initiating layer (photopolymerization initiator comprising a monomer and/or an oligomer) in a condition contacting with a hydrophilic monomer to make a hydrophilic polymer graft on the lower layer surface (see, e.g., JP-A No.10-53658). In this technique, however, there is a problem in that, since the photopolymerization initiator is not firmly fixed in the photopolymerization initiating layer, the initiator contained in the initiation layer is dissolved in a hydrophilic monomer solution during surface graft polymerization, and as a result, polymerization occurs in the hydrophilic monomer solution to yield a homopolymer as a by-product, which has not been bonded to the initiation layer for photopolymerization, on the surface of the layer. Because of this problem, a part of the polymer terminal in the generated polymer cannot be chemically bonded to the substrate, and dampening water tends to be invited into the image area of the planographic printing plate precursor, whereby insufficient adhesion between the recording layer and the substrate occurs so as to decrease printing performance, and especially press life.
In another method, a photopolymerization initiator-fixed layer is formed with a photopolymerization initiator bonded to a polymer, on which a hydrophilic surface graft layer is formed as a hydrophilic layer (see, e.g., JP-A No.11-43614). The present inventors have examined this method and found that there is a problem in that, when graft polymerization is carried out by contacting a monomer solution with a photopolymerization initiating layer to form a hydrophilic layer, the initiator component contained in the initiating layer is dissolved in the monomer solution, and as a result, polymerization occurs in the hydrophilic monomer solution to yield a homopolymer on the surface of the layer as a by-product which has not been bonded to the initiating layer for polymerization. Because of this problem, a portion of the polymer chain terminals in the generated polymer cannot be chemically bonded to the substrate, and dampening water tends to be invited into the image area, whereby insufficient adhesion between the recording layer and the substrate occurs so as to decrease printing performance, especially press life.
The pattern of hydrophilicity/hydrophobicity has been utilized in a variety of fields. In particular, in the printing industry, and particularly in the field of planographic printing, a planographic printing plate precursor has been known, which can be used in printing directly after exposure, without requiring any complicated wet development process, by controlling the hydrophilicity/hydrophobicity of the surface to form a desired pattern.
As a planographic printing plate precursor to which such a pattern consisting of hydrophilicity/ hydrophobicity has been applied, a positive planographic printing plate precursor which is prepared by crosslinking a polymer containing a group thermally convertible from a hydrophobic group to a hydrophilic group, such as a sulfonic acid ester group or an alkoxyalkyl ester group, is proposed in JP-A No.11-84658. Additionally, JP-A No.7-1849 proposes a negative planographic printing plate precursor in which microcapsules containing a hydrophobic composition that can react with a hydrophilic group are dispersed in a crosslinked hydrophilic layer.
In these planographic printing plate precursors, since the image-recording layer has a crosslinking structure, the image area and non-image area are not formed by removal of the corresponding area of image recording layer, but rather by change of the polarity of the surface, and thus, the plate is of non-treating type requiring no development treatment.
In these planographic printing plate precursors of the surface polarity-changing type, it is considered that a water-holding capacity of the non-image area is necessary in order to generate the hydrophilicity with no scumming at printing. For that purpose, it is considered that the polarity change is required to occur to some depth of non-image area, and not only at the surface. Therefore, in the above-mentioned sensitive materials, much higher energy is required to cause the polarity change in the depths of non-image area, and a usual amount of image recording energy sometimes results in low sensitivity. In order to raise the sensitivity at usual amount of image recording energy, making an image recording layer thinner has been considered, but in conventional planographic printing plate precursors, when the thickness is reduced, the water-holding capacity is reduced so as to provide a product that is worse with respect to scumming property. Therefore it has been impossible to sufficiently discriminate the hydrophilicity and the lipophilicity. Further, a thinner layer causes another problem in that the preess life of the planographic printing plate is deteriorated.
In order to solve the problems, a method for raising the water-holding capacity by forming an image-recording layer comprising graft polymer having a polarity-changing group through a photopolymerization initiating layer on a support has been proposed. In such a planographic printing plate precursor, however, there is a problem in that, at the time of graft polymerization, an initiator contained in the initiating layer is dissolved in the monomer solution when the monomer solution having a polarity-changing group is contacted with the photopolymerization initiating layer. As a result, polymerization occurs in the monomer solution, and homopolymers, which have not been bonded to the initiating layer, are yielded on the surface of the layer as a by-product. Moreover, there is an another problem in that the homopolymers are released from the image-recording layer at printing so as to disturb stable supply of printed matter.
Further, JP-A No. 11-43614 proposes a technique for immobilizing a photopolymerization initiator in a photopolymerization initiating layer using a photopolymerization initiator bonded to a polymer. In this method, however, there is also a problem in that it is not possible to completely prevent dissolution of the photopolymerization initiator in the photopolymerization initiating layer, and as a result, a homopolymer is yielded as a by-product.
Hitherto, a variety of members having surface layers with various functions which are prepared by adsorbing functional particles on optional substrates have been proposed. Examples of the members having the particle-adsorbed surface layers include antireflection members on which unevenness is provided using resin or metal particles, conductive members on which electrically conductive particles are adsorbed, anti-pollutive and anti-bacterial members on which anti-bacterial metal (oxide) particles are adsorbed, gas-barrier films which lower gas transparency utilizing a laminated structure of particles, and shading members made with particle materials which block ultraviolet rays, infrared rays or visible light. In addition, the members in which particles are adsorbed on the surface are involved in an important technique which permits a high degree of functionalization such as considerable expansion of the surface area, elevation of image resolution and increase of the density of materials used in catalysts, recording materials, sensors, electronic devices, optical devices, etc. Under such circumstances, studies of such techniques have actively been made.
The following describes typical members whose surface are roughed with particles, which members are useful as antireflection materials for controlling the refraction index of the surface to prevent light reflection because they have predetermined small unevenness.
Further, in recent years, image displays typified by liquid crystal displays (LCD), plasma display panels (PDP), cathode-ray tube displays (CRT), electroluminescence (EL) lamps, and the like have widely been used in televisions, computers, and a variety of recently prevalent mobile devices and have experienced remarmable development. High image quality, reduction of electricity consumption, and so on, have been demanded of such displays, accompanying functional improvement in a variety of devices in which the displays are used. With respect to improvement of image quality, it is an important factor to prevent reflection of light such as that from lighting on the surface of a display, i.e., antireflection, in addition to improvement of the pixel density of images and realization of clear color tone.
In particular, mobile terminal displays which have rapidly become precalent in recent years are naturally expected to be used outdoors. Therefore, it has been necessary to develop a highly antireflective display in which reflection of outdoor light such as sunlight or fluorescence can be prevented.
In addition, LCDs which are characterized by being lightweight, compact and generally versatile have widely been used. In mobile devices equipped with such an LCD (portable terminal), input of touch-panel type, i.e., a system of handling in which an operation is carried out by directly touching a specified region on the display surface with a plastic pen or finger, has widely been employed. Therefore, it is important that, in addition to high image quality and anti-reflectiveness, the surface of the display has characteristics such as endurance, e.g.,acrassion resistance, as well as grim resistance.
As a method of providing an antireflective capability, conventionally, it has been common to make the incidence plane for light rough to scatter or diffuse light. The rough surface is formed by direct roughening of the substrate surface by means of sand blasting, embossing, etc., or by coating a coating solution containing a filler on the substrate surface followed by drying to form a rough layer.
In particular, a method for forming a rough layer containing a filler on the substrate surface is now used widely because it is easy to control unevenness on the rough surface and permit easy production. Specifically, for example, JP-A No.6-18706 has proposed a roughened layer which comprises a UV-cured resin and resinous beads in order to apply the same to a less thermostable and highly transparent plastic film.
In the method of using a roughened layer containing a filler, however, there has been a problem in that the unevenness formed with the filler is negated by the effect of a binder making it difficult to achieve the antireflection capability as designed since the filler forming unevenness is immobilized on the substrate with a binder. When the binder is diluted or the amount of the binder to be used is reduced in order to improve the effect of unevenness of the filler, the strength of the film may be reduced resulting in a problem with durability.
In addition, as another known method for providing an antireflection capability, a highly refractive material is laminated in alternation with a low refractive material to form a multi-layered antireflection layer. The formation of the multi-layer structure may specifically carried out by a vapor phase method such as alternate vapor deposition of a low refractive material, e.g. SiO2, and a highly refractive material, e.g. TiO2, or ZrO2, to form film, or by a sol-gel method utilizing hydrolysis of a metal alkoxide and condensation polymerization.
In these methods for forming a multi-layered antireflection layer, a gas phase method such as vapor deposition requires an expensive processing apparatus and is not appropriate for production of layers with a large area. In the case of the sol-gel method, there are problems in that the repetitive coating and burning raises the cost of production and the produced antireflection layer exhibits a violet or green tint making spots stand out.
In addition, another method for providing an antireflection capability has been proposed in N. J. Nattan, M. Brust et al., “Chemical Materials”, 2000, (Vol) 12, (R) 2869, wherein negatively charged colloid gold particles are adsorbed on the surface of a silicone oxide substrate and immobilized with aminopropanethiol as a linker to form a crosslinking structure, which operation is repeated several times to adsorb gold particles adsorb on the substrate surface to form a multi-layer. In such a method, it is possible to produce an antireflection member having a roughened layer in which gold particles are adsorbed on the substrate. This technique, however, requires a complicated process and it is difficult to practically apply this technique to formation of particle-adsorbed layers.
As illustrated above by examples of members having an antireflection capability, it has been difficult to form a highly durable functional surface layer having varried functionality. Particularly, when a coating method is used in order to form a functional surface layer, it has been difficult to induce the function as initially designed because the function of the functional particles is blocked by a binder.
Presently, a thin layer film in which metal particles have been dispersed is now actively being used in a variety of fields. In one known method, a thin layer film is produced by “coating particles on the surface of a substrate, followed by coating a polymer thereon” (for example, ANDREW J. KELLOCK, “Journal of Colloid and Interface Science”, 1993, (Vol) 156, (pp) 240–249). This method, however, is complicated since it requires execution of 3 steps, i.e., 1. production of particles; 2. coating of the particles; and 3. coating of a polymer. In addition, there is a problem in this method in that the ratio of the particles to be contained in the film is limited to several % by mass and it is difficult to exhibit the particulate characteristics. Moreover, there is a problem in that adhesion of the particles is poor since the particles are immobilized only by being coated on a substrate, and as a result, the durability of the metal particle-dispersed thin layer film is poor.